The spinal column of bones is highly complex anatomical structure that includes over 20 bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction. The more than 20 discrete bones of an adult human spinal column are anatomically categorized as one of four classifications—cervical, thoracic, lumbar, or sacral—and are coupled together sequentially to one another by a tri-joint complex that consists of an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs or vertebrae. The cervical portion of the spine comprises the top of the spine up to the base of the skull and includes the first seven vertebrae. The intermediate 12 bones are thoracic vertebrae, and connect to the lower spine comprising the 5 lumbar vertebrae. The base of the spine comprises sacral bones, including the coccyx. With its complex nature, however, there is also an increased likelihood that surgery may be needed to correct one or more spinal pathologies.
Genetic or developmental irregularities, trauma, chronic stress, tumors and disease can result in spinal pathologies that either limit this range of motion or that threaten critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve this immobilization by implanting artificial assemblies in or on the spinal column. These assemblies may be classified as anterior, posterior, or lateral implants. Lateral and anterior implants are generally coupled to the anterior portion of the spine that is in the sequence of vertebral bodies. Posterior implants generally comprise pairs of rods, which are aligned along the axis that the bones are to be disposed, and that are then attached to the spinal column by hooks that couple to the lamina, hooks that attach to the transverse processes, or by screws that are inserted through pedicles. The orientation of each of these rods, however, are often limited by the alignment of the one or more screws they are affixed to.
Therefore, it is desirable, during surgical implantation of such posterior devices, to have a modular head-to-head cross connector that allows for percutaneous delivery, independent alignment between pairs of rods and fastener screw, and improved reliability, durability, and ease of installment of said devices.